JPH0756477B2 - Insertable sensor probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an insertion type sensor used for measuring the concentration of hydrogen or water vapor in high temperature exhaust gas discharged from a boiler, a sintering furnace, an automobile or the like. The present invention relates to a probe, and more particularly, to an insertion type sensor probe that uses a solid reference material as a reference for galvanic electromotive force.

[Prior Art] Measuring the concentration of hydrogen and water vapor in high temperature exhaust gas is
It is indispensable for accurately obtaining the combustion efficiency of boilers, combustion furnaces, automobile engines, etc. Therefore, there is a demand for the development of a highly reliable hydrogen and water vapor concentration measuring device that operates stably in high-temperature exhaust gas.

Therefore, conventionally, there has been proposed a hydrogen or water vapor sensor which uses a proton conductive solid electrolyte made of a perovskite type oxide such as strontium oxide and cerium oxide (SrCeO ₃ ) as a sensor element (JP-A-58-5).
0458,60-263853,61-2064,61-3054,61-14566).
This solid electrolyte has proton conductivity at a temperature of 300 ° C. or higher, and a sensor element made of this solid electrolyte is formed into a closed type, and the inner surface and the outer surface thereof are covered with a porous inner electrode and outer electrode, respectively. It is configured to wear. A reference gas that serves as a reference for galvanic electromotive force, that is, a gas containing hydrogen or water vapor at a predetermined concentration is enclosed in the sensor element.

When a sensor probe that measures the concentration of hydrogen or water vapor using this perovskite-type proton conductive solid electrolyte is inserted into the gas to be measured, the difference in hydrogen or water vapor concentration between the reference gas and the gas to be measured causes An electromotive force is generated between the electrode and the outer surface electrode. Then, by detecting this electromotive force, the concentration of hydrogen or water vapor in the gas to be measured can be measured.

However, since the above-mentioned conventional technique uses a gas containing a predetermined concentration of hydrogen or water vapor as a reference substance,
There are the following problems.

When the solid electrolyte, the gas introduction pipe, or the like is damaged, the reference gas leaks into the measurement atmosphere, and the measurement becomes impossible or a measurement error occurs. Further, in this case, the leaked reference gas pollutes the measurement atmosphere.

In order to supply the reference gas to the probe and circulate it, a gas circulator or the like is required, and a compact device cannot be obtained.

Therefore, the present inventors have developed a solid reference material that exhibits a stable hydrogen activity at high temperatures, and have proposed using this solid reference material for a hydrogen or water vapor sensor (Japanese Patent Laid-Open No. 63-269053).

[Problems to be Solved by the Invention] However, particularly in the case of an insertion-type hydrogen or water vapor sensor that is installed by being inserted in a measurement atmosphere, the sensor itself is exposed to high temperatures, so that the solid reference substance and the measurement atmosphere It is difficult to completely seal the space. Therefore, the insertion type hydrogen or water vapor sensor using this solid reference material has not been put to practical use.

The present invention has been made in view of such problems,
In the insertion type hydrogen or water vapor sensor used at high temperature, the solid reference substance can be sufficiently sealed from the measurement atmosphere, and this solid reference substance can be used practically even at high temperature. An object of the present invention is to provide an insertable sensor probe that can eliminate the drawbacks of the sensor using the.

[Means for Solving the Problems] An insertion type sensor probe according to the present invention is a sensor element of one-end closed type formed of a perovskite type proton conductive solid electrolyte, and a galvanic electromotive force reference filled in the sensor element. A solid reference material, a reference electrode formed on the inner surface of the sensor element in contact with the solid reference material, and a measurement electrode formed on the outer surface of the sensor element,
A ceramic holder, one end of which is closed to fit and hold the sensor element at the other end side, and at least the space between the inner surface of the ceramic holder and the outer surface of the sensor element is hermetically sealed to seal the both. A solid reference material and a seal part for isolating the reference electrode from the measurement atmosphere, and the seal part has a coefficient of thermal expansion of 300 to 800 ° C.
It is characterized by being 8.0 × 10 ^{−6 to} 10.0 × 10 ⁻⁶ / ° C.

[Operation] In the present invention, the one-end closed sensor element is held by the ceramic holder on the other end side, and the seal portion is interposed between the ceramic holder and the sensor element. The solid reference material with which the element is filled is hermetically sealed from the measurement atmosphere outside the sensor element by the ceramic holder and the seal portion together with the reference electrode inside the sensor element. The seal part has a thermal expansion coefficient of 8.0 × 10 ^{-6 to} 10.0 × 10 ^-6 / ° C in the temperature range of 300 to 800 ° C, which is the operating temperature of the sensor.
It has substantially the same thermal expansion coefficient as the solid electrolyte having a thermal expansion coefficient of 10 ^-6 to 9.8 × 10 ^-6 / ° C.. Therefore, when the probe is placed in a high-temperature measurement atmosphere, even if the solid electrolyte constituting the sensor element thermally expands, the seal portion also thermally expands to the same extent as the sensor element. No gas will enter the inside of the sensor due to a gap between the seal portion and the sensor element or damage to the solid electrolyte. Therefore, the solid reference substance inside the sensor element can be reliably sealed and protected from the measurement atmosphere.

Also, if a dense glass sealing material with a pour point equal to or higher than the sensor operating temperature is used for this seal part, this seal part has excellent heat resistance at the sensor use temperature and has sufficient strength without fluidization. Therefore, a precise seal structure can be formed. Further, this dense glass sealing material has no reactivity with the solid electrolyte that constitutes the sensor element,
Moreover, the wettability with the solid electrolyte is excellent and the bondability is good.

The proton conductive solid electrolyte is Ca, Sr and B.
at least one element selected from the group consisting of a
As a component, at least one element selected from the group consisting of Ce, Zr, Ti and Hf is used as a B component, and Yb, Y, Sc, Zn, Nd, Mg, I
When M component is at least one element selected from the group consisting of n, Sm, Dy, Eu, Ho, Gd, Tm, Ca and La, the general formula
It is a perovskite complex oxide represented by AB _1-X M _X O _3-Y . However, both X and Y are numerical values in the range of 0 to 0.5.

Examples of such perovskite-type composite oxides include, for example, SrCe _0.95 Yb _0.05 O _3-Y , BaCe _0.9 Nd _0.1 O _3-Y and CaZr _0.9.
In _0.1 O _3-Y, etc.

EXAMPLES Examples of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a sensor probe according to a first embodiment of the present invention. The sensor element 1 has a tubular shape with one end closed, and a measuring electrode 3 and a reference electrode 4 are formed by depositing a porous material on the outer surface and the inner surface of approximately half of the closed end side. The measurement electrode 3 and the reference electrode 4 cover approximately half of the sensor element 1 on the closed end side. The sensor element 1 is filled with a solid reference material 2, and the solid reference material 2 is enclosed in the sensor element 1 so that a cylindrical shape is formed in approximately half of the open end side of the sensor element 1. An eggplant ceramic chip 5 is inserted.

A lead wire 8 connected to the reference electrode 4 is inserted through the center of the ceramic chip 5, and the reference electrode 4 is electrically led out of the sensor element 1 by the lead wire 8. A metal paste 6 is interposed between the ceramic chip 5 and the inner surface of the sensor element 1.

Then, a ceramic holder 9a is fitted to approximately half of the sensor element 1 on the open end side. This ceramic holder 9a
Has a tubular shape whose inner diameter is larger than the outer diameter of the sensor element 1 and which is closed at one end, and is fitted onto the sensor element 1 with the open end of the sensor element 1 in contact with the inner end surface of the ceramic holder 9a. . A hole is formed at the center of the ceramic holder 9a, and the lead wire 8 is inserted through this hole and led out to the outside. A paste-like glass seal material is filled between the inner peripheral surface of the ceramic holder 9a and the outer surface of the sensor element 1 to form a seal portion 7a, whereby the solid reference substance 2 and the reference electrode 4 are formed. It is hermetically sealed from the outside world and the measuring electrode 3. The inner surface of the ceramic holder 9a has a slightly larger diameter on the open end side, which facilitates fixing between the ceramic holder 9a and the sensor element 1 with a paste-like glass sealing material.
Further, the inside of the center hole of the ceramic holder 9a through which the lead wire 8 is inserted is also sealed by the paste-like glass sealing material.

The sensor element 1 is SrCe _0.95 Yb _0.05 O _3-Y , CaZr _0.9 In _0.1 O _3-Y ,
It is molded with a proton conductive solid electrolyte composed of a perovskite type complex oxide such as BaCe _0.95 Y _0.05 O _3-Y .

The reference electrode 4 and the measurement electrode 3 are formed by baking a porous material such as Pt, Ni or an oxide conductor.

Further, as the solid reference substance 2, for example, there is a mixture of Ni powder with a mixed salt of cerium sulfate and an alkali carbonate. The ceramic chip 5 acts as a plug for enclosing the solid reference substance 2 in the sensor element 1, and serves as a partition wall for separating the glass sealant and the solid reference substance 2 from each other in order to prevent them from fusing at high temperature. To work.

Furthermore, the metal paste 6 is interposed between the ceramic chip 5 and the inner surface of the sensor element 1 in order to secure electrical conduction between the porous reference electrode 4 and the lead wire 8. The metal paste 6 contains Pt, Ni, or the like, has electrical conductivity, and is applied to the peripheral surface of the ceramic chip 5 and then the ceramic chip 5 is fitted into the sensor element 1 so that a space between the two is obtained. Intervened.

As the lead wire 8, an ordinary conductor wire such as a Pt wire or a Ni wire may be used.

As the pasty glass sealing material forming the glass sealing portion 7a, a dense glass having a composition such as Na ₂ O ₃ · B ₂ O ₃ · SiO ₂ may be used. In this case, the dense glass should have a coefficient of thermal expansion of 8.0 × 10 ^{-6 to} 10.0 × 10 ^-6 / ° C in the temperature range of 300 to 800 ° C and a pour point of not less than the sensor operating temperature. select. This paste-like glass sealing material is applied, for example, to the inner surface of the ceramic holder 9a, the sensor element 1 is further inserted into the ceramic holder 9a, and then heated at 850 ° C. in an electric furnace to be fused. It can be attached to the ceramic holder 9a and the sensor element 1.

The ceramic holder 9a is made of ceramic such as alumina or mullite.

In the insertion-type sensor probe configured as above, when the tip portion of the sensor element 1 formed of the solid electrolyte is inserted into the measurement atmosphere, the outer surface of the solid electrolyte that comes into contact with the measurement atmosphere containing hydrogen or water vapor. The protons move between the solid reference substance 2 and the inner surface of the solid electrolyte in contact with the solid reference substance 2 due to the difference between the concentration of hydrogen or water vapor in the measurement atmosphere and the reference concentration of the solid reference substance 2. A galvanic electromotive force is generated between the measurement electrode 3 and the reference electrode 4 due to the movement of the protons. By detecting this electromotive force via the lead wire 8 or the like, the hydrogen or water vapor concentration in the measurement atmosphere can be detected.

In this case, in the present embodiment, the solid reference substance 2 and the reference electrode 4 are hermetically sealed by the seal portion 7a interposed between the sensor element 1 and the ceramic holder 9a into which the open end is fitted. Since the solid reference material 2 and the reference electrode 4 are housed in the sensor element 1, the solid reference material 2 and the reference electrode 4 are shielded from the measurement atmosphere so that gas in the measurement atmosphere does not enter. Therefore, even if this sensor probe is inserted into the measurement atmosphere, the solid reference material 2 does not react with the gas in the measurement atmosphere to change its concentration.

The seal portion 7a has a coefficient of thermal expansion of 8.0 × 10 ^{−6 to} 10.0 × 10 ⁻⁶ / ° C. in the temperature range of the sensor probe used in the range of 300 to 800 ° C., and the thermal conductivity of the solid electrolyte constituting the sensor element 1 is increased. It has a coefficient of thermal expansion similar to that of the expansion coefficient (8.5 × 10 ^{−6 to} 9.8 × 10 ⁻⁶ / ° C.). Further, the ceramic holder 9a also has a thermal expansion coefficient similar to that of the solid electrolyte forming the sensor element 1. Therefore, even if the sensor probe is inserted into a high-temperature measurement atmosphere, cracks may occur in the seal portion 7a or the sensor element 1 due to the difference in thermal expansion coefficient between the seal portion 7a and the sensor element 1, or Peeling does not occur.
Therefore, the solid reference material 2 can be completely sealed by the sealing portion 7a even at high temperature.

Further, since the seal portion 7a is formed of dense glass (Na ₂ O ₃ , B ₂ O ₃ , SiO _2, etc.) having a pour point higher than the sensor operating temperature, the sensor operating temperature of 300 to 800 ° C It does not fluidize in the region, has sufficient strength, is dense and has sufficient heat resistance. Further, this type of glass does not react with the solid electrolyte, its properties are not deteriorated, and the wettability with respect to the solid electrolyte and the ceramic is good, so that the sensor element 1 and the ceramic holder which are the solid electrolyte are formed. 9a is applied with sufficient strength.

FIG. 2 is a sectional view showing another embodiment of the present invention. This embodiment differs from the embodiment shown in FIG. 1 only in the insertion position of the ceramic chip and the shape of the ceramic holder, and the other construction is the same. Is omitted.

That is, the ceramic chip 5 is inserted deeper into the sensor element 1 than in the case of the embodiment shown in FIG. Also,
The ceramic holder 9b has a conical shape with which the end edge of the sensor element 1 fitted inside contacts. A hole for inserting the lead wire 8 extends from the apex of this cone to the outer surface of the ceramic holder 9b.

The paste-like glass sealing material is provided outside the region between the inner surface of the ceramic holder 9b and the outer surface of the sensor element 1, the portion of the sensor element 1 on the open end side of the ceramic chip 5 and the inner side surface of the ceramic holder 9b. The area formed by is also filled, and the seal portion 7b is provided in a vast area.

As described above, in this embodiment, since the paste-like glass sealing material is packed inside the sensor element 1, the sensor element 1 is adhered not only to the outer surface but also to the inner surface thereof. Therefore, in the present embodiment, the glass sealing material can be provided so as to be further in close contact with the sensor element 1 as compared with the case of the first embodiment in which the glass sealing material is applied only to the outer surface of the sensor element 1. .

Next, the results of actually measuring the concentrations of hydrogen and water vapor using the sensor probe according to the present embodiment described above will be described.

Measurement of Hydrogen Concentration A sensor probe having the structure shown in FIG. 2 was used. The sensor element 1 of this sensor probe is formed of a perovskite type proton conductive solid electrolyte having a composition of SrCe _0.95 Yb _0.05 O _3-Y . The outer diameter of this sensor element 1 is 4m.
m, inner diameter 2.5 mm, length 20 mm. This sensor element 1
Platinum porous electrodes on the inner and outer surfaces (4 reference electrodes, 3 measurement electrodes)
After baking at 900 ° C., the solid reference material 2 adjusted to a predetermined composition was filled in the sensor element 1 in a length of 10 mm.
Then, a platinum paste 6 was applied to a mullite chip (ceramic chip 5) through which a Pt wire having a wire diameter of 0.2 mm was passed and inserted into the sensor element 1. The diameter of this mullite tip is
The length is 2 mm and the length is 10 mm. Then, the composition is Na ₂ O ₃ · B ₂ O ₃ ·
A ceramic holder made of SiO ₂ paste glass sealant
After coating the inside of 9b, attach the sensor element 1 to the ceramic holder 9b.
The inside of the sensor element 1 was filled with a glass sealing material. This glass sealant has a coefficient of thermal expansion of 9.5 × 10 ^-6 /
), The softening point is 695 ° C, and the pour point is 880 ° C. The assembly thus assembled was loaded into an electric furnace and heated, and the pasty glass sealing material was fused to the sensor element 1 and the ceramic holder 9b to form a probe. In this case, the heating rate and the cooling rate in the electric furnace are both 5
C./min. And held at 850.degree. C. for 10 minutes.

Next, a part of this sensor probe was inserted into the alumina insertion tube 10 and fixed with an inorganic adhesive 12 so that the part of the measurement electrode 3 was exposed to the outside. A print lead wire 11 electrically connected to the outer surface measurement electrode 3 of the sensor probe is formed by baking platinum paste on the outer surface of the insertion tube 10. Also, the outer diameter of the insertion tube 10 is
6.5mm, inner diameter is 4.5mm, length is 300mm. Then, this sensor probe was inserted and installed in the furnace core tube 22 of the tubular furnace 21 shown in FIG. In the tubular furnace 21, the hydrogen gas and the nitrogen gas supplied from the hydrogen gas cylinder 24 and the nitrogen gas cylinder 25 are mixed in a gas mixer.
The gas is once collected in 23, mixed in a predetermined mixing amount in the gas mixer 23, and then introduced into the furnace core tube 22 via a pipe 29. A thermocouple 26 is installed in the furnace core tube 22.
Is inserted, and the output of the thermocouple 26 is input to and recorded in the analyzing recorder 27. As a result, the temperature in the vicinity of the sensor element 1 in the furnace core tube 22 is measured and recorded. Further, the gas in the furnace core tube 22 is taken out from the lower end portion of the furnace core tube 22 and supplied to the gas chromatograph analyzer 28.

Using the device configured as described above, the relationship between the hydrogen partial pressure and the electromotive force in the sensor probe was determined. However, the atmospheric temperature in the furnace core tube 22 heated by the tubular furnace 21 is 700 or 800 ° C., and the amount of hydrogen is 0.1 to 10 by the gas mixer 23.
The range was 0%.

The result is shown in FIG. The horizontal axis of FIG. 5 is the hydrogen partial pressure measured by the gas chromatograph analyzer 28, and the vertical axis is the galvanic electromotive force generated between the measurement electrode 3 and the reference electrode 4 of the sensor probe. However, the horizontal axis of FIG. 5 is a logarithmic scale. The ambient temperature was 700 or 800 ° C. as described above, and the ambient temperature was adjusted to a constant value by detecting the ambient temperature with the thermocouple 26 and feeding back the detection result to the control of the drive power of the tubular furnace 21.

As is clear from FIG. 5, there is a linear relationship with good linearity between the logarithm of the hydrogen partial pressure and the electromotive force. Therefore, as shown in FIG. 5, the relationship between the known hydrogen partial pressure at a specific atmospheric temperature and the electromotive force is obtained in advance, and this is used as the calibration, and the measured value of the electromotive force is used to measure the atmosphere. The amount of unknown hydrogen in it can be measured.

Measurement of Water Vapor Concentration Next, the result of measuring the amount of water vapor using the apparatus shown in FIG. 6 will be described. This apparatus supplies steam into the furnace core tube 22 from its head through a pipe 34. Constant temperature bath 30
A constant temperature medium 31 having a temperature near the boiling point of water is stored therein, and a buffler 32 is immersed in the constant temperature medium 31. Then, water is stored in the baffler 32, and compressed air is introduced into the buffler 32 from the air pump 33, so that the steam generated in the buffler 32 is sent to the pipe 34, and this steam is supplied to the furnace through the pipe 34. It is adapted to be supplied into the core tube 22. The amount of water vapor was defined by the temperature in the constant temperature bath 30.

As a result of measuring the amount of water vapor using the apparatus configured as described above, as shown in FIG. 7, the measurement result of the amount of water vapor also showed excellent linearity between the water vapor partial pressure _PH20 and the electromotive force. A relationship was obtained. Therefore, also with respect to this water vapor, by previously obtaining the relationship between the water vapor amount and the electromotive force at a specific temperature, the water vapor amount in the measurement atmosphere of unknown water vapor concentration can be measured based on this.

[Effects of the Invention] According to the present invention, the reference electrode and the solid reference substance can be reliably sealed from the measurement atmosphere even at a high temperature. Therefore, the sensor using the solid reference substance should be used for the measurement of hydrogen or water vapor. Therefore, unlike the conventional sensor using a reference gas as a reference substance, a device for circulating the reference gas is not required, and a small and highly reliable insertion type sensor probe can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a sensor probe according to an embodiment of the present invention, FIG. 2 is a sectional view showing a sensor probe according to another embodiment of the present invention, and FIG. 3 is incorporated with this sensor probe. A side view showing the detection member, FIG. 4 is a schematic diagram showing a hydrogen concentration analyzer, FIG. 5 is a graph showing the results of the hydrogen concentration analysis, FIG. 6 is a schematic diagram showing a water vapor concentration analyzer, and FIG. The figure is a graph showing the results of the water vapor concentration analysis. 1; sensor element, 2; solid reference material, 3; measuring electrode, 4; reference electrode,
5; Ceramic chip, 7a, 7b; Seal part, 9a, 9b; Ceramic holder

Claims (4)

[Claims] 1. A sensor element of one-end closed type formed of a perovskite type proton conductive solid electrolyte, a solid reference substance filled in the sensor element and serving as a reference of galvanic electromotive force, and an inner surface of the sensor element. A reference electrode formed in contact with the solid reference material, a measurement electrode formed on the outer surface of the sensor element, and a ceramic holder that is closed at one end and holds the sensor element by fitting the other end side. And a sealing portion which is filled at least between the inner surface of the ceramic holder and the outer surface of the sensor element and hermetically seals both of them to isolate the solid reference material and the reference electrode from the measurement atmosphere, The sealing portion has a thermal expansion coefficient of 300 to 800 ° C. of 8.0 × 10 ^{−6 to} 10.0 × 10 ⁻⁶ /
Insertable sensor probe characterized by being at a temperature of ℃. 2. The insertion type sensor probe according to claim 1, wherein the seal portion is a dense glass seal material having a pour point equal to or higher than a sensor use temperature. 3. The perovskite-type proton conductive solid electrolyte is a composite oxide of strontium and cerium,
The insertion-type sensor probe according to claim 1 or 2, wherein the main component is any one selected from the group consisting of a complex oxide of barium and cerium and a complex oxide of calcium and zirconium. . 4. The perovskite-type proton conductive solid electrolyte contains at least one element selected from the group consisting of indium, scandium, ytterbium, magnesium, bismuth, aluminum, gallium, yttrium and neodymium. The insertion type sensor probe according to claim 3.